This invention relates to the field of blood processors which are routinely used during a medical operation to salvage blood shed by a patient and to reinfuse or store that blood after it has been filtered and cleaned. Apheresis refers to the procedure in which a portion of the blood (plasma, platelets, etc.) is separated and either returned or disposed of and the remainder (red blood cells, white blood cells, etc.) is reinfused into the patient or off-line stored. Blood transmitted diseases, such as AIDS and hepatitis, caution against utilizing blood from third parties unless absolutely necessary. Blood washers have been developed to collect, clean and filter the patient's blood and then return it to the patient.
Typically, during an operative procedure, varying amounts of blood will be shed by a patient. This blood must be removed from the operative site to allow the physician to work, usually by a suctioning wand which aspirates blood, particulates and other fluids (such as irrigating or wash fluid) from the operation site. The suctioned blood can be either discarded or else cleaned, filtered and returned to the patient. After an operation has been performed, blood may continue to be collected through an incision in the patient's body. This blood, referred to as post-operatively shed blood, may also be cleaned and filtered and returned to the patient.
Products on the market today range from simple filtration devices which remove large particulate matter to relatively expensive hardware devices coupled to disposable components which collect, hold, and then clean and filter the blood. An example of such a device is the Cell Saver.TM. device marketed by Haemonetics Corporation. The Haemonetics device is comprised of a blood collection chamber and a disposable component. The Haemonetics hardware is a relatively expensive apparatus and the disposable components moderately priced. The disposable is used for a single procedure. It is then discarded after the blood has been separated into blood fluids and cellular components and then is discarded, while the hardware is used for a number of procedures again and again.
There are also many simple devices for blood processing which comprise a receptacle to receive salvaged blood and a filter which filters out particulate matters greater than the size of the filter pores. Once the blood has been filtered of particulate matter, it is then reinfused into the patient. A blood filtering device of this type is disclosed in U.S. Pat. No. 4,033,345, issued on Jul. 5, 1977 to Sorenson et al. Blood from a wound site in the Sorenson et al. device is suctioned into a receptacle and passed through a number of filters prior to reinfusing the filtered (but not separated into components) blood into a patient.
In addition to merely filtering, as is performed in simple filtering devices referred to above, it is often desirable to separate the blood components. Blood is composed of cellular blood components and blood fluids, among other things. Blood cell separation eliminates a large percentage of the plasma (as a fluid) contained in the blood, along with undesirable contaminants (such as irrigating or wash fluids and anticoagulant fluids) and returns only red blood cells to the patient. Whereas simple filtration devices referred to above eliminate large-sized particulate matter, plasma and all other components of blood are permitted to be reinfused into the patient.
Another shortcoming of a simple filtration device is that it allows undesirable micromolecular entities such as free hemoglobin and cell wall remnants that are smaller than the pore size of the filter to pass through the filter and be reinfused into the patient. The desirability of efficient filtering and washing of blood is hampered by the costs of large cell washers, such as the Haemonetics CellSaver.TM.. The physician may then be left to the inefficiency of a simple filtering mechanism. In operative procedures in which the amount of shed blood is expected to be of a smaller volume, in the range of one or two units, the use of a conventional cell washer is not cost-effective. Simple filtration devices may be used in these circumstances, with the inherent problems discussed above, or else the blood may be disposed of and the patient reinfused with a third party's blood. This latter action increases the likelihood of a blood carried disease or immunological complication being transmitted to the patient.
Another disadvantage of presently available products is that, in the case of cell washers, personnel must be trained in the operation of the relatively complex device. Furthermore, the expense of complex cell washing devices limits their use in orthopedic and other procedures or else forces the physician, due to cost constraints, to use simple filtration systems which have the disadvantages discussed above.
In addition, some prior art devices have sophisticated controls or many moving parts which may be subject to wear or breakage. For example, U.S. Pat. No. 4,935,002, issued to Gordon, discloses a device for collecting, processing and then returning blood to a patient. One embodiment disclosed in the Gordon patent utilizes a rotating disk which performs the function of filtering and applying shearing forces to separate red blood cells from the remaining blood products such that red blood cells only pass through the filter. The Gordon device requires a motor to drive the rotating disk and discloses a microprocessor which controls various pumps which pump blood, wash solution and anticoagulant solution into the filtration system.
In U.S. Pat. No. 5,055,198 issued to Shettigar, an autologous blood recover membrane system and method is disclosed. In the Shettigar device, blood from a suction source is passed through a first filter and then, under the influence of a roller pump, blood passes through a membrane filter which separates blood fluids from red blood cells. The Shettigar device also provides for a recirculation of blood to the first filter to provide further filtering. In the Shettigar device, washing fluid is admixed with blood from the wound site prior to introduction into the first filter. A hematocrit monitor connected in line with the membrane filter will cause the blood, dependent on the hematocrit level of the blood, to either recirculate through the filter once again or to be reinfused into the patient. While Shettigar discloses a number of embodiments for his invention, the device is necessarily relatively expensive and complex.
U.S. Pat. No. 4,631,050 to Reed et al. is directed to an autotransfusion system and method. Reed discloses an autotransfusion system which consists of a first filter chamber to remove large particles which is in turn connected to an ultrafiltration unit. Blood which has been filtered by the first unit then passes through the ultrafiltration unit. In order to increase the rate at which blood fluids pass through the ultrafiltration filter, the ultrafiltration unit is pressurized on the side in which the blood fluid products are introduced, thus causing blood fluid products to pass through the filter and for red blood cells remaining on the filtration side to be siphoned off. The washed and concentrated blood cells are then reinfused to the patient. The Reed disclosure also provides for the introduction of a washing solution into the ultrafiltration cell unit to aid in the washing of the blood.
U.S. Pat. No. 4,886,487 to Solem et al. discloses a autotransfusion device in which blood is siphoned from a patient, mixed with an anticoagulant solution and then introduced into a first particulated filter where a wash solution is added. A roller pump pumps the wash solution and blood through a second filter which separates blood fluids from red blood cells and returns the red blood cells to the patient. A vacuum source is required to withdraw the suctioned blood from the patient site into the first filter and a roller pump is required to pump the filtered blood through the second separation filter. All of the above prior art devices require various controls and motors to cause filtration and separation of blood components.